Adam, an architectural engineer with university education, designed the Ponderosa's ranch house.
Despite the show's high ratings and critical success during his time as Adam, Roberts grew wary of Bonanza. The workload of cranking out 34-episode seasons for NBC came into play, as did Adam and his brothers' dependence on their father, Ben Cartwright (Lorne Greene).
"Isn't it just a bit silly for three adult males to get Father's permission for everything they do?," Roberts asked the Washington Post in 1986. "I have an impotent role. Everywhere I turn, there's the father image."
Frustrations about his character and other issues found Roberts miserable when it came time to film new episodes.
"I was in the series for six years. I fought with the powers about the scripts, character development and other things. It got so I was upset the minute I arrived for work. That's no way to live," he explained a year after leaving the show (as quoted by the Washington Post). "I don't have the psychological stamina to last under artistic compromises over a prolonged period of time. I get hostile and vindictive. It wears me down."
After Roberts left the series, Adam was written off as being at sea. Bonanza TV movies from the '90s go a step further, explaining that Roberts relocated to Australia.
Pernell Elven Roberts Jr. was born on May 18, 1928 in Waycross, Georgia. His earliest breaks as an actor came in plays, including roles in Broadway and off-Broadway productions. Among these plays were Camelot and other musicals that showcased Roberts' musical talents.
All four main Bonanza cast members recorded music, with Roberts as the most experienced singer.
His Hollywood film debut came alongside Burl Ives in Desire Under the Elms (1958). That same year, Roberts appeared with Shirley MacLaine in The Sheepman. A year later, he co-starred in Lee Van Cleef's Ride Lonesome.
Additional film roles range from the star-studded The Magic of Lassie (1978) to cult favorites Four Rode Out (1969) and The Kashmiri Run (1970). TV movie roles include 1989's The Night Train to Kathmandu, alongside a young Milla Jovovich.
Roberts' post-Bonanza career included more than just a return to theater. His TV show filmography on IMDB lists appearances on The Virginian, Mannix, Mission: Impossible, Vega$, Ironside, San Francisco International Airport and Marcus Welby, M.D.
Of course, Roberts got a second run as a network TV superstar in CBS' M*A*S*H spinoff Trapper John, M.D. (1979-'86). He played title character John McIntyre twice as long as Wayne Rogers did on the original M*A*S*H TV series and, in the process, became an Emmy nominee.
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Roberts died on Jan. 24, 2010 in Malibu, California after a battle with pancreatic cancer. He was survived by his fourth wife, Eleanor Criswell.
"On the set of 'Bonanza,' he protested the use of all-white crews and guest stars, finding some support but never enough to satisfy his sense of outrage," a statement from his family read (as quoted by BET).